Datasheet

LT3055
12
3055f
For more information www.linear.com/LT3055
PIN FUNCTIONS
REF/BYP (Pin 11): Bypass/Soft-Start. Connecting a capaci-
tor from this pin to GND bypasses the LT3055’s reference
noise and soft starts the reference. A 10nF bypass capaci-
tor typically reduces output voltage noise to 25μV
RMS
in
a 10Hz to 100kHz bandwidth. Soft-start time is directly
proportional to BYP/SS capacitor value. If the LT3055 is
placed in shutdown, BYP/SS is actively pulled low by an
internal device to reset soft-start. If low noise or soft-start
performance is not required, this pin must be left floating
(unconnected). Do not drive this pin with any active cir-
cuitry. Because the REF/BYP pin is the reference input to
the error amplifier, stray capacitance at this point should
be minimized. Special attention should be given to any
stray capacitances that can couple external signals onto
the REF/BYP pin producing undesirable output transients
or ripple. A minimum REF/BYP capacitance of 100pF is
recommended.
GND (Pin 12, Pin 13, Exposed Pad Pin 17): Ground.
The exposed pad of the DFN and MSOP packages is an
electrical connection to GND. To ensure proper electrical
and thermal performance, solder Pin 17 to the PCB ground
and tie it directly to Pins 12, 13. Connect the bottom of
the output voltage setting resistor divider directly to GND
(Pin 12) for optimum load regulation.
IN
SHDN
3055 F01
R
P
OUT
V
IN
SENSE
GND
LT3055
R
P
+
+
+
LOAD
Figure 1. Kelvin Sense Connection
ADJ (Pin 14): Adjust. This pin is the error amplifier’s invert-
ing terminal. The typical bias current of 15nA flows out
of the pin (see the ADJ pin Bias Current vs Temperature
curve in the Typical Performance Characteristics section).
The ADJ pin voltage is 600mV referenced to GND.
Connecting a capacitor from ADJ to OUT reduces output
noise and improves transient response for output voltages
greater than 600mV. See the Applications information sec-
tion for calculating the value of the feedforward capacitor.
OUT (Pins 15,16): Output. These pins supply power to
the load. Stability requirements demand a minimum 3.3μF
ceramic output capacitor with an ESR < 1Ω to prevent
oscillations. For output voltages less than 1.2V, a mini-
mum 4.7µF ceramic output capacitor is required. Large
load transient applications require larger output capaci-
tors to limit peak voltage transients. See the Applications
Information section for details on output capacitance and
reverse output characteristics. Permissible output voltage
range is 600mV to 40V.